*{
    /*让元素的width包括border和padding*/
    box-sizing: border-box;
}
body{
    margin: 0;
    padding: 0;
    font-size: 14px;
    color: gray;
}
header{
    line-height: 240%;
    background-color: gold;
    color: white;
    text-align: center;
    font-weight: bold;
    font-size: 18px;
}
form{
    /*border: 1px solid red;*/
    padding: 10px;
}
input{
    display: block;
    width: 100%;
    /*如果让子元素离父元素有个间距，一般选用设置父元素的padding,而不是操作子元素的margin*/
    /*margin-left: 10px;
    margin-right: 10px;*/
    height: 40px;
    padding-left: 10px;
    margin-bottom: 10px;
    border: 1px solid gold;
    border-radius: 10px;
    color: gray;
}
input[type="submit"]{
    background-color: gold;
    /*border: 1px solid gold;*/
    color: white;
    font-size: 18px;
    font-weight: bold;
}
footer{
    font-size: 20px;
    font-weight: bold;
    text-align: center;
    display: none;
}